In-situ balancing of plated polymers

ABSTRACT

A method for balancing a rotatable component is disclosed This method comprises and then plating the component to deposit a metal layer onto the component until the component is balanced. In addition, and alternative method for balancing a rotatable component is disclosed. This method comprises attaching a balancing weight to the rotatable component and rotating the component. This is followed by plating the component and the balancing weight to deposit a metal layer onto the balancing weight and the component until the component is balanced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application Ser. No. 61/844,030 filed on Jul. 9,2013.

FIELD OF THE DISCLOSURE

This disclosure relates to methods for the in-situ balancing of platedpolymers. More specifically, this disclosure relates the balancing arotatable component in place by rotating the component and brush platingor brush electroplating a metal layer onto the component until thecomponent until it is balanced. Additionally, this disclosure relatesthe in-situ balancing of rotatable components by attaching a balancingweight to component, rotating the component, and then brush plating orbrush electroplating the component and balancing weight until thecomponent is balanced.

BACKGROUND

Metallic parts tend to be heavy due to the high densities of mostmetals. Typically, there are areas of a metallic part that are lightlyloaded or not loaded (little or no stress) as well as highly loaded (orstressed) areas. An ideal metallic part would contain a sufficientamount of metal in high-stress areas to transmit the necessary loads andperform the function of the part. Such an ideal part would also containless or no metal in areas with little or no stress, thereby reducing theweight of the metallic part to an idealized minimum. In some cases,removing metal from a metallic part can lead to weight savings. However,removing metal from a metallic part by conventional means, such asmachining, laser drilling, etc., can be both difficult and costly.Further, removing material from a metallic part can lead to reducedmaterial properties of the part, which may be unacceptable for itsintended application. Therefore, there is a need for improved and/orlower-cost methods of producing metal parts that are lightweight butstrong enough in high-stress areas to perform the function(s) of thepart.

There is an ongoing effort to replace metal components in a gas turbineengine with lighter components made from alternative materials, even ifthe components experience significant loads or are subjected toenvironmental concerns (e.g., high or low temperatures, erosion,foreign-object damage) during use. For example, in the aerospaceindustry, manufacturers of gas turbine engines are considering the useof alternative materials for fan blades, compressor blades, and possiblyturbine blades. Suitable non-metal alternative materials include, butare not limited to, reinforced polymers, polymer matrix composites,ceramics, and ceramic matrix composites.

Blow molding processes begin with melting the molding material andforming it into a parison or preform. The parison is a tube-like pieceof plastic with a hole in one end through which compressed air can passthrough. The parison is clamped into a mold and air is pumped into theparison. The air pressure pushes the molding material outwards to matchthe interior surface of the mold. Once the molding material has cooledand hardened, the mold opens and the part is ejected. In contrast,injection molding includes injecting molding material for the part intoa heated barrel, mixing and forcing the molding material into a moldcavity where the molding material cools and hardens to the configurationof the cavity. Compression molding is a method of molding in which thepreheated molding material is placed in an open-mold cavity. The mold isclosed and pressure is applied to force the material into contact withall mold areas while heat and pressure are maintained until the moldingmaterial has cured.

For many molding processes, hard tooling is used to form the mold ordie. While hard tooling can provide high dimensional repeatability, hardtooling is very heavy and cumbersome and can present a safety hazardwhen moved or handled. Further, fabricating hard tooling is timeconsuming and costly. As a result, hard tooling is normally tooexpensive and time consuming for short production runs and/or for thefabrication of test parts. Thus, the ability to quickly fabricatetooling to support short production runs and/or test runs of compositematerials is desired.

Blow molding and injection molding cannot be used if the plastic to bemolded is in the form of a composite with a plurality of layers orplies, i.e., a composite layup structure. Composites are materials madefrom two or more constituent materials with different physical orchemical properties that, when combined, produce a material withcharacteristics different from the individual components. The individualcomponents remain separate and distinct within the finished structure.Typically, composite layup structures can be molded or shaped usingcompression molding, resin transfer molding (RTM), or vacuum assistedresin transfer molding (VARTM), all of which utilize hard tooling thattypically include details machined into one or more blocks of metal thatform the mold.

Composites can also include reinforcing fibers or matrices. The fibersor matrices may be formed from ceramics, metals, polymers, concrete, andvarious other inorganic and organic materials. Organic matrix composites(OMCs) may include polyimides and/or bismaleimides (BMIs) because theycan be used at higher temperatures than other commonly used organicreinforcing materials, such as epoxies. Such high-temperature OMCs maybe processed by autoclave molding, compression molding, orresin-transfer molding. These processes all require lengthy cure andpost-cure cycles as well as hard tooling that is difficult and costly tomake. Thus, improved methods for molding OMCs are also desired.

Electrolytic and electroless plating are inexpensive methods of forminga metallic layer on a surface of a molded plastic article. To ensureadhesion of the plated layer to the molded plastic article, the surfaceof the plastic article may need to be prepared by etching, abrading, orionic activation. The most common types of metals used for platingmolded plastic include copper, silver, and nickel, although other metalsmay be used.

Electrolytic plating is the deposition of a metal on a conductivematerial using an electric current. A molded plastic article must firstbe made conductive to be electrolytically plated. This can be donethrough a multi-step process that typically involves the application ofa catalyst, electroless plating of Ni, and electrolytic plating of Cu.The article to be electrolytically plated is then immersed in a solutionof metal salts connected to a cathodic current source, and an anodicconductor is immersed in the bath to complete the electrical circuit.Electric current flows from the cathode to the anode, and the electronflow reduces the dissolved metal ions to pure metal on the cathodicsurface. Soluble anodes are made from the metal that is being plated anddissolve during the electroplating process, thereby replenishing thebath.

A closely related process is brush electroplating, in which localizedareas or entire items are plated using a brush saturated with platingsolution. The brush may be a stainless steel body wrapped with a clothmaterial that both holds the plating solution and prevents directcontact with the item being plated. The brush may be connected to thepositive side of a low-voltage direct-current power source, and the itemto be plated connected to the negative side. The operator dips the brushin plating solution then applies it to the item to be plated, moving thebrush continually to get an even distribution of the plating material.Brush electroplating has several advantages over tank plating, includingportability, ability to plate items that for some reason cannot be tankplated (e.g., plating portions of very large decorative support columnsin a building restoration), low or no masking requirements, andcomparatively low plating solution volume requirements. Disadvantagescompared to tank plating can include greater operator involvement (tankplating can frequently be done with minimal attention), and inability toachieve a plate as thick as can be achieved using tank plating.

Measuring strain on rotating components has historically beenproblematic and involves sending data out to stationary data acquisitionsystems via split-ring electrical coupling or radio frequency (RF)transmission devices. Strain gages, the associated wiring, and/or themass and volume of a radio transmitter can interfere with the operationof a component, especially if balancing is critical, if the spaceenvelope surrounding the component is tight, or if airflow over asurface of the component is involved. Measuring strain on rotatingcomponents is important to accurately assess component failure, whetherit is made from a traditional alloy or from an aforementionedalternative material.

Plated polymeric mechanical test specimens are needed to accuratelycharacterize the stress and strain imposed on a plated polymericstructure. Test specimens that are completely encapsulated in metalplating are not preferred because such an encapsulated specimen does notsimulate a semi-infinite medium, which best approximates plated polymerwalls in actual parts. It is more helpful to cut test specimens out oflarger plated panels to provide exposed edges (a sandwich structure)approximating a semi-infinite medium. Preliminary testing of platedpolymers demonstrates that tensile testing of thick-plated polymerscannot be reliably accomplished by gripping standard test specimengeometries, such as the test specimens specified by ASTM D638. Grippinga standard, plated test specimen results in either (1) too much slippageto accurately or reliably calculate ultimate load, displacement, andstrain values, or (2) the test specimen being crushed in the gripregion, resulting in stress concentrations, significant strain outsideof the gage area, and premature failure.

Therefore, there is a need for improved methods and apparatuses formeasuring strain imposed on parts, including rotating components, thatmay be made from alternative materials such as polymers, reinforcedpolymers, polymer matrix composites, ceramics, and ceramic matrixcomposites.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a method for balancing arotatable component is disclosed. The method may comprise, rotating thecomponent and plating the component to deposit a metal layer onto thecomponent until the component is balanced.

In a refinement, the plating may be selected from the group consistingof brush plating and brush electroplating.

In another refinement, the brush plating may comprise a brush saturatedwith plating solution.

In another refinement, the brush may be selected from the groupconsisting of stainless steel or graphite.

In another refinement, the brush may be further wrapped with a clothmaterial that holds the plating solution and prevents direct contactwith the part being plated.

In another refinement, the brush electroplating may comprise a brushsaturated with plating solution.

In another refinement, the brush may be selected from the groupconsisting of stainless steel or graphite.

In another refinement, brush may be further wrapped with a clothmaterial that holds the plating solution and prevents direct contactwith the part being plated.

In accordance with another aspect of the present disclosure, a methodfor balancing a rotatable component is disclosed. The method maycomprise attaching a balancing weight to the rotatable component,rotating the component, and plating the component and the balancingweight to deposit a metal layer onto the balancing weight and thecomponent until the component is balanced.

In a refinement, the plating may be selected from the group consistingof brush plating and brush electroplating.

In another refinement, the brush plating may comprise a brush saturatedwith plating solution.

In another refinement, the brush may be selected from the groupconsisting of stainless steel or graphite.

In another refinement, the brush may be further wrapped with a clothmaterial that holds the plating solution and prevents direct contactwith the part being plated.

In another refinement, the brush electroplating may comprise a brushsaturated with plating solution.

In another refinement, the brush may be selected from the groupconsisting of stainless steel or graphite.

In another refinement, the brush may be further wrapped with a clothmaterial that holds the plating solution and prevents direct contactwith the part being plated.

In another refinement, the balancing weight may be selected from thegroup consisting of metals, metal powder filled resins and polymers.

In accordance with another aspect of the present disclosure, a methodfor balancing a rotatable fan assembly is disclosed. The method maycomprise attaching a balancing weight to a fan assembly, rotating thefan assembly, followed by plating the fan assembly and the balancingweight to deposit a metal layer onto the balancing weight and fanassembly until the fan assembly is balanced.

In a refinement, the balancing weight may be selected from the groupconsisting of metals, metal powder filled resins and polymers.

In another refinement, the plating may be selected from the groupconsisting of brush plating and brush electroplating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flow diagram illustrating the disclosed methods of forminglightweight metal parts.

FIG. 1B illustrates, schematically, various means for joining two moldedpolymeric components together prior to plating.

FIG. 2 is a perspective view of a rotating fan assembly that is coupledto a strain measurement system in accordance with this disclosure,wherein the strain measurement system is shown schematically.

FIG. 3 is a side sectional view of a fan assembly coupled to a disclosedstrain measurement system, which is shown schematically.

FIG. 4 is a plan view of a test specimen made in accordance with ASTMD638, Type IV, but with holes extending through both grip portions.

FIG. 5 is a plan view of one layer of a composite layup structure havingthe shape of the test specimen shown in FIG. 4, but with reinforcingfibers, and particularly illustrating the arrangement of the reinforcingfibers so they extend around one of the holes in the grip portion and sothat the fibers are not cut when the hole is made. The left side of FIG.5 illustrates the cutting of longitudinally arranged fibers when thehole is made.

FIG. 6 is another plan view of at least one layer of a composite layupstructure, wherein the layer includes reinforcing fibers and thereinforcing fibers are arranged to extend around the holes disposed inthe grip portions so that the fibers are not cut once holes are made.

FIG. 7 is another plan view of at least one layer of a composite layupstructure, wherein the layer includes reinforcing fibers that arearranged to avoid the areas where the holes are subsequently made,thereby avoiding cutting of the reinforcing fibers that extend throughthe gauge region.

FIG. 8 is another plan view of at least one layer of a composite layupstructure, when the layer includes reinforcing fibers that are disposedtransversely to the longitudinal direction of the layer.

FIG. 9 is another plan view of at least one layer of a composite layupstructure, wherein the layer includes reinforcing fibers that extendaround both holes in the grip portions of the layer and proceed towardsa corner of the respective grip portion at an angle of about 45° withrespect to a longitudinal axis that proceeds through the gauge region.

FIG. 10 is another plan view of at least one layer of a composite layupstructure that is similar to FIG. 9 but with an opposite configurationand therefore portions of the fibers extending through the grip portionsand past the holes would be disposed transversely to the correspondingfiber portions shown in FIG. 9.

FIG. 11 is another plan view of at least one layer of a composite layupstructure, wherein the layer includes reinforcing fibers disposed atabout a 45° angle with respect to a longitudinal axis passing throughthe gauge region.

FIG. 12 is another plan view of at least one layer of a composite layupstructure, wherein the layer includes reinforcing fibers disposed atabout a 45° angle with respect to a longitudinal axis passing throughthe gauge region, but transversely with respect to the fibersillustrated in FIG. 11.

FIG. 13 is another plan view of at least one layer of a composite layupstructure, when the layer includes reinforcing fibers that extendlongitudinally through the layer.

While the exemplary rotating component shown in the drawings is a fanblade assembly, it will be apparent to those skilled in the art that thedisclosed strain measurement system and methods of measuring strainimparted to a rotating component may be utilized in connection withcompressor blades, turbine blades, propeller blades, wheels, or othercomponents that may be fabricated from non-traditional, non-metal, oralternative materials that are subject to strain when the component isrotated.

DETAILED DESCRIPTION Lightweight Parts and Components Produced fromPlating Molded Polymeric Substrates

FIG. 1A illustrates various disclosed methods for forming lightweightparts and components in accordance with this disclosure. In part 11, apolymer is selected for forming a desired shape or geometry from whichthe part will be created. Typically, the polymer will be acrylonitrilebutadiene styrene (ABS), polytetrafluoroethylene (PTFE), or anABS/polycarbonate blend. These polymers are mentioned here because theyare compatible with most etching solutions. However, other polymers thatare compatible with the selected etching solution or other evacuationmethod may be utilized, as will be apparent to those skilled in the art.In part 12, the polymer is formed or molded into the desired shape orgeometry for the metal structure.

The forming of the polymer may be carried out in any of a variety ofways, such as additive manufacturing, injection molding, compressionmolding, blow molding, extrusion molding, thermal forming, transfermolding, reaction injection molding, and, if applicable, combinationsthereof, or other suitable forming process as will be apparent to thoseskilled in the art. In part 13, if necessary, the outer surface of theformed polymer may be prepared for receiving a catalyst for thesubsequent plating process(es). The outer surface may be prepared in avariety of ways, such as etching, abrading, reactive ion etching, ionicactivation, deposition of a conductive material such as graphite, silverpaint, gold sputter, etc. and, to the extent applicable, combinationsthereof.

The metals used for plating may include nickel, cobalt, iron, copper,gold, silver, palladium, rhodium, chromium, zinc, tin, cadmium, andalloys of the foregoing elements comprising at least 50 wt. % of thealloy, although other metals can be used. The plating process can beextended to a range of non-metal substrates, including, but not limitedto, polymer, reinforced polymer, polymer matrix composite, ceramic,ceramic matrix composite, etc.

In part 14, the outer surface of the formed polymer may be activated byapplying a catalyst. Typically, the catalyst is palladium althoughplatinum and gold are other possibilities. The catalyst may be appliedto a thickness on the atomic scale. Prior to the application oractivation with the catalyst, the formed polymer may be rinsed orneutralized, especially if an etching process is carried out. Subsequentto the activation with a catalyst, an accelerator may be optionallyapplied. In part 15, a first layer of metal is deposited onto the outersurface of the formed polymer using an electroless plating method.Typically, the metal used to form the first layer via electrolessplating is nickel, although copper, gold, and silver are otherpossibilities. After the first layer is formed on the outer surface ofthe formed polymer to form a metal structure, if the desired thicknessfor the metal structure has not been reached or additional materialproperties are desired, a second layer of metal may optionally bedeposited on the first layer by electrolytic plating in part 16. If thesecond layer is not to be succeeded by a third layer, the second layermay be formed from a metal that is the desired material for the finishedpart.

Electrolytic plating is the deposition of a metal on a conductivematerial using an electric current. A component made from a non-metalmaterial must first be made conductive to be electrolytically plated.This can be done through electroless plating or by the use of conductiveadditives such as carbon. The article to be electrolytically plated isimmersed in a solution of metal salts connected to a cathodic currentsource, and an anodic conductor is immersed in the bath to complete theelectrical circuit. Electric current flows from the cathode to theanode, and the electron flow reduces the dissolved metal ions to puremetal on the cathodic surface. Soluble anodes are made from the metalthat is being plated, thereby replenishing the bath.

The polymer may be evacuated after the first or second layers aredeposited, but it may be preferable to apply successive layer(s) ofmetal to the structure wherein the successive layer(s) may be formedfrom a metal that is the desired material for the finished part. Theapplication of the optional successive layer(s) of desired material maybe carried out in a variety of ways including, but not limited toelectroplating, electroless plating, electroforming, thermal spraycoating, plasma vapor deposition, chemical vapor deposition, coldspraying, and other techniques that will be apparent to those skilled inthe art. The successive layer(s) of desired metal may be applied in part17 as shown in FIG. 1A. In part 18, at least one hole may be formedthrough the structure for purposes of evacuating the polymer in part 19,unless such a hole is an integral feature of the structure. The hole maybe formed after formation of the first layer, optional second layer,optional successive layer, or at any time after the structure issufficiently strong. The hole may be patched at part 20 prior to a finalheat treatment or prior to the application of additional metallic layersin part 21. A final heat treatment can be carried out at part 22 or thelayer(s) may be alloyed via a bonding treatment, such as transientliquid phase (TLP) bonding, brazing, diffusion bonding, or otheralloying means known to those skilled in the art.

The final metallic part may be hollow or may be filled with areinforcing filler material or the polymeric article may be of astructure that has material properties to render it suitable forremaining within the final metallic part in a partially etched orremoved state. Suitable materials for such reinforcing filler materialare a metallic or polymeric foam, although other suitable fillermaterials will be apparent to those skilled in the art.

Anti-Counterfeiting Tags

Counterfeiting has a long and ignoble history, ranging from art andliterature to manufactured goods, particularly replacement parts.Further, counterfeiting in the aerospace, automotive, or othertransportation industries, for example, may have serious consequences asthe use of an inferior counterfeit replacement part may create a safetyhazard. Thus, there is a need to effectively reduce the introduction ofcounterfeit parts into supply chains in general and a more urgent needto reduce the presence of counterfeit parts in supply chains ofindustries where the use of counterfeit parts creates safety concerns.

An anti-counterfeiting tag may be added to a plated polymeric articleand therefore the final part. In such an embodiment, theanti-counterfeiting tag should be detectable through the platedstructure by an appropriate sensor. Such anti-counterfeiting tags mayinclude a material of a different density than the polymer(s) used tofabricate the article, a low-level radioisotope, an RFID tag that isdetectable through the plated metal structure, a particular chemicalthat can be sensed in the molded plastic article and through the platedmetal structure, or another identifier useful for anti-counterfeitingpurposes as will be apparent to those skilled in the art.

If the article is molded, the anti-counterfeiting tag may be co-moldedwith the article or a protrusion can be included in the mold tool toprovide a recess for housing the anti-counterfeiting tag. Alternatively,a slot can be machined in the polymeric article using any manufacturingprocess to allow for the anti-counterfeiting tag. A polymeric plug maybe bonded over the exposed surfaces of the anti-counterfeiting tag toprovide a completely polymeric surface for post plating. In anotherembodiment, the article may be a polymeric composite layup structurewith a plurality of plies or layers and the anti-counterfeiting tag maybe disposed between adjacent plies or layers of the layup structure.

Composite Molded Polymeric Articles

As noted above, the shaped polymeric article may be for use as a moldand can be formed using one of the molding processes described above andwhich can be plated with at least one metallic layer to form aninexpensive metal tooling that can be economically used to support shortproduction runs and/or the fabrication of test parts or components. Theshaped polymeric article may also be base for a gauge, other instrumentor prototype hardware that can be fabricated by coating the shapedpolymeric article with one or more metallic layers.

When the plated polymer component is used for tooling, it may beadvantageous to form the article with a composite layup structure formedfrom one or more of the following: polyetherimide (PEI); polyimide;polyether ether ketone (PEEK); polyether ketone ketone (PEKK);polysulfone; nylon; polyphenylsulfide; polyester; and any of theforegoing with fiber reinforcement e.g., carbon fiber, glass-fiber, etc.The composite layup structure may be compression molded into a desiredshape to from a composite article. One or more metallic layers may bedeposited onto the composite article to form a structure. If thestructure is to be used as tooling for a short term production or forthe production of test parts, the metallic layer(s) may applied byelectroless plating, electroplating, or electroforming with a thicknessranging from about 2.54 to about 1270 microns (about 100 to about 5e+004microinches), more typically from about 101.6 to about 1016 microns(about 4000 to about 4e+004 microinches). This thickness range mayprovide sufficient resistance to wear and impact, and/or provide theability to meet tight tolerance requirements and/or provide a surfacefinish that will be transferred to the molded part.

The plated metallic layer(s) that forms the tooling structure mayinclude one or more layers. Plating may be performed in multiple stepsby masking certain areas of the molded article to yield differentthicknesses or no plating in certain areas. A customized platingthickness profile can also be achieved by tailored racking (includingshields, thieves, conformal anodes, etc.). Tailored racking allows foran optimization of properties for the mold tooling with respect to heatresistance, structural support, surface characteristics, etc. withoutadding undue weight to the tooling to completely accommodate each ofthese properties individually. Plating thicknesses may be tailored tothe structural requirements of the mold tooling.

Some mounting features (e.g., flanges or bosses) may be bonded to themolded article using a suitable adhesive after molding but beforeplating to simplify the mold tooling. Further, the polymer or compositearticle can be fabricated in multiple segments that are joined by anyconventional process (e.g., by welding, adhesive, mitered joint with orwithout adhesive, etc.) before plating. Furthermore, molded compositearticles may be produced and plated separately and subsequently bondedby transient liquid phase (TLP) bonding. In addition, features such asbosses or inserts may be added (using an adhesive, riveting, etc.) tothe plated structure or tooling after the plating has been carried out.When the molded article is to be used as a substrate formed by injectionmolding and to be plated for use in a tooling, the article may have athickness ranging from about 1.27 to about 6.35 mm (about 0.05 to about0.25 inch), with localized areas ranging up to 12.7 mm (0.5 inch). Incontrast, compression molding can be used to form a molded article witha wall thicknesses ranging from about 1.27 to about 51 mm (about 0.05 toabout 2.008 inch).

For some parts with complex geometries and/or that are large,multiple-piece mold toolings are required because the molded part cannotbe reliably released from a single mold. Thus, to fabricate tooling forsuch a part with complex geometry and/or that is large, the part may bedivided into a plurality of segments, which may be coupled. Possibleweak points caused by the joining of two segments together may beovercome by joining the two segments using one or more joints incombination an adhesive that remains within the joint so that theadhesive is not exposed to or “visible” to a subsequent plating process.The types of joints that may be suitable for coupling two such polymersegments together include mitered joints, angled joints, angled-miteredjoints, welded joints with covers, mitered joints with low angleboundaries, mitered joints with accommodation channels for accommodatingextra adhesive, welded joints with a cover, slot-type attachments withour without an additional fastener, and others as will be apparent tothose skilled in the art. Then, the two segments are plated togetherusing one of the plating methods described above. By plating one or morelayers over the joint and over the outer surfaces of two segments,possible structural weak points created by the coupling of the twosegments are avoided. Suitable adhesives include epoxy-based adhesivesin liquid, paste, or film form, with long-term service temperatures ofup to 121° C. (249.8 degree Fahrenheit), and bismaleimide-basedadhesives with service temperatures of up to 177° C. (350.6 degreeFahrenheit) (in paste or film form). In addition, cyanoacrylates andpolyurethanes could be used in certain situations, depending upon thestrength and rigidity requirements.

The plating material and thickness may be selected such that astructural analysis would indicate that the plating layer will take themajority of the loads that the part experiences. Furthermore, geometricfeatures are optionally added into the design to mitigate any weaknesscaused by the joining to two segments together prior to the plating.

Temporary or short-run tooling may be made using the disclosed methods,particularly if the molded article is fabricated from a composite layupstructure that is sufficiently stiff, but which can be compressionmolded. The compression molded composite article serves as a substratethat may be plated to form a tooling.

Plating of Joined Polymeric Articles

Conventional processes for fabricating polymeric parts (e.g., injectionor compression molding) have limitations with respect to geometriccomplexity and part size. In particular, large parts (by volume orweight) may exceed the capabilities of available injection moldingmachines or compression presses. Complex geometry or features within apart may also make it difficult to form and successfully release thepart from the mold tooling. Complex geometries or features may alsorequire very intricate multi-piece mold designs.

Therefore, an ability to fabricate separate part details and join theminto an assembly may offer cost benefits in these situations. By platinga polymeric part with a suitable plating material to a suitablethickness, the structural weak points that are caused by bonding may beovercome.

An exemplary substrate may be a molded structure formed of at least onematerial selected from the group consisting of: polyetherimide (PEI);polyimide; polyether ether ketone (PEEK); polysulfone; Nylon;polyphenylsulfide; polyester; and any of the foregoing with fiberreinforcements e.g., carbon fibers or glass-fibers. Suitable adhesivesfor joining the molded substrates include epoxy-based adhesives inliquid, paste or film form, with long-term service temperatures foraerospace applications of up to 250° F. (121° C.), and bismaleimide(BMI) based adhesives in paste or film forms with service temperaturesof up to 350° F. (177° C.). Also, cyanoacrylates and polyurethanes couldbe used in selected cases depending on strength and rigidityrequirements.

Plating on adhesives can be difficult and causes deviations in platingproperties. FIG. 1B schematically illustrates a variety of methods orjoints that can be used to join polymeric substrate segments together sothat bond line effects are minimized and only the polymeric material isvisible to the plating process. The methods or joints include, but arenot limited to a mitered joint 31, an angled joint 32, an angled miteredjoint 33, a welded joint 34 with covers 35 that may be press-fit intoplace or secured with adhesive or weld beads 36, a mitered joint 37 withlow angle boundaries, a mitered joint 38 with accommodation channels 39for extra adhesive, a slot attachment-type joint 41, a welded T-joint 42with a cover 43, a mitered joint 44 attached with a fastener 45, andothers as will be apparent to those skilled in the art. Further, twocomponent halves may be joined to create one or more tortuous passages.Also, components with ducts of different cross sections may beeconomically molded and joined together. Any combination of these andsimilar methods can be used to create plated polymeric parts withgeometries and/or sizes that are outside the limits or economicfeasibility of conventional molding processes.

The plating material and thickness may be selected such that astructural analysis indicates that the plating layer will take themajority of the loads that the part experiences. Furthermore, geometricfeatures are optionally added into the design to mitigate the bond lineproperty knockdowns.

Thus, plated polymeric parts can be produced on a larger scale than thecapacity limits of injection or compression-molding processes currentlyallow. Part geometries for plated polymeric parts can be morecomplicated than the injection or compression-molding processes canallow. Part cost can be reduced when complex parts that are difficult tomold are molded in multiple, simpler segments. The plating material andthickness are selected to accommodate weaknesses induced by bond linesand bonding methods.

Polyimide and Bismaleimide Resins

High temperature organic matrix composites (OMCs) such as polyimides andbismaleimides (BMIs) are typically formed into a desired shape byautoclave molding, compression molding or resin-transfer molding. Thesemolding processes all require lengthy cure and post-cure cycles as wellas costly mold toolings, which have long lead times. These moldingmethods are also limited in terms of the geometrical complexity of thedesired shape of the molded article.

Additive manufacturing (AM) or three-dimensional (3D) printing is aprocess of making a three-dimensional solid object of virtually anyshape from a digital model. AM is achieved using an additive process,wherein successive layers of material are laid down in different shapes.AM is considered distinct from traditional machining techniques, whichmostly rely on the removal of material by methods such as cutting ordrilling, i.e., subtractive processes. A materials printer usuallyperforms AM processes using digital technology. Since the start of thetwenty-first century there has been a large growth in the sales of thesemachines, and while the price has dropped substantially, AM remains verycostly. Despite its high cost, AM is used in many fields, includingaerospace.

In the disclosed methods, imidized polyimide resin and/or bismaleimideresin (BMI) may be used to form desired shapes by additive manufacturing(AM). The resins may be solids at room temperature and may be ground andsieved to the appropriate size for powder bed processing (SLS) or thesolid resin can be melted for liquid bed processing (SLA). The resultingAM article can then be plated to provide additional strength, thermalcapability, erosion resistance, etc., and combinations thereof. Theplating layer may include one or more layers. The metallic layer may beapplied by electroless plating, electroplating, or electroforming. Oneespecially useful application is for wear parts such as bushings,liners, and washers, which have extensive applications in gas turbineengines and in other manufacturing industries.

Strain Measurement on Non-Metal Components with Plated Targets

FIG. 2 illustrates a fan blade assembly 110 that is coupled to a strainmeasurement system 111. The fan blade assembly 10 includes a pluralityof fan blades 112 that are coupled to a rotor or disk 113. To saveweight, the fan blades 112 may be fabricated from non-metallicmaterials, such as polymers, reinforced polymers, polymer matrixcomposites, ceramics, ceramic matrix composites, etc.

However, because failure of a fan blade 112 of a fan blade assembly 110of a gas turbine engine presents a safety hazard, measuring the strainimposed on the fan blades 112 during rotation of the fan blade assembly110 may be desirable. FIG. 2 therefore illustrates schematically astrain measurement system 111 that includes a first encoder 114 (orother suitable type of sensor), a second encoder 115 (or other suitabletype of sensor), a controller 116, which may be integrated with thefirst and second encoders 114 and 115, respectively, a firstelectromagnetic target 117 disposed on the fan blade 112 and a secondelectromagnetic target 118, also disposed on the fan blade 112 andspaced apart from the first electromagnetic target 117 by a distanceshown as D. The first and second electromagnetic targets may be platedonto the fan blade 112.

When the fan blade 112 is stationary, or is otherwise not undersignificant strain or stress, the first and second electromagnetictargets 117, 118 are spaced apart by an initial distance D₁. As the fanblade assembly 110 is rotated, the centrifugal forces experienced by thefan blade 112 may impart strain to the fan blade 112 thereby changingthe distance between the first and second electromagnetic targets 117and 118, respectively from the initial distance D₁ to an actual distanceD₂. The first and second encoders 114 and 115, respectively, aredesigned to monitor the actual positions of the first and secondelectromagnetic targets 117 and 118, respectively. Those actualpositions may be transmitted to the controller 116, which may be aseparate component or which may be integral with the first and secondencoders 114 and 115, respectively. The controller 116 may have a memory119 that may be programmed with at least one program for determining theactual distance D₂ based upon the signals received from the first andsecond encoders 114 and 115, respectively. The memory 119 of thecontroller 116 may also be programmed with an algorithm for calculatingstrain imparted to the fan blade 112 during rotating thereof based onthe differences between the actual distance D₂ and the initial distanceD₁. Information relating to the strain imparted to the fan blade 112 maythen be transmitted to the operator or pilot of the aircraft or the maincontrol module of the aircraft.

FIG. 3 illustrates the fan blade assembly 110 as disposed within anacelle 121. FIG. 2 also partially illustrates the rotor 113 coupled toa nose cone 122. It will be noted that the encoders 114 and 115 may bedifferent types of sensors and/or may incorporate Hall-effect sensors aswell. If the encoders/sensors 114 and 115 incorporate Hall-effectsensors, the encoders/sensors 114 and 115 may also measure therotational velocity of the fan blade 112.

Strain Measurement on Thick, Plated Polymer and/or Composite Components

Preliminary testing of plated polymers has demonstrated that tensiletesting of thick-plated polymers cannot be reliably accomplished byusing conventional gripping techniques on grip portions of standard testspecimen geometries. This conventional method produces either (1) fartoo much slippage to accurately or reliably calculate ultimate load,displacement, and strain values, or (2) crushes the test specimen in thegrip area, resulting in stress concentrations, significant strainoutside of the gage area, and premature failure.

Using a 30% carbon-fiber-reinforced amorphous thermoplastic(polyetherimide, commonly known as ULTEM®) with 0.008 in (0.2 mm(0.007874 inch)) nominal Ni plating, the amount of slippage could beneglected for a Type IV specimen tested in accordance with the ASTM D638protocol. In contrast, using a Type IV specimen and testing under ASTMD638 and with a 0.015 in (0.38 mm (0.01496 inch)) nominal Ni plating,the amount of slippage was severe enough that absolute displacement (andtherefore strain) values could not be accurately obtained. As a solutionto this problem, a pin-loaded tensile specimen in accordance with ASTMD638, Type IV may be used, preferably with two spaced-apart holesdrilled therein to allow for pin loading of the specimen. For example,referring to FIG. 4, the overall length of the specimen 200 may be about12.7 cm (5 inches) and the centers of the holes 201 may be spaced apartby about 9.616 cm (3.786 inches). The holes may have about a 0.653 cm(0.2571 inch) diameter and may be centered longitudinally in the widerend portions or the grip regions 202 of the Type IV specimen 200. Thegrip regions 202 may have a width of about 1.91 cm (0.752 inch). Thearcs 203 connecting the grip regions 202 to the narrow middle gaugeregion 204 may have a radius of about 2.54 cm (1 inch). The length ofthe middle gauge region 204 may be about 3.175 cm (1.25 inches).

The hole 201 sizes may be optimized using certain parameters. Forexample, plating thickness, width of the gage region, hole diameter, andwidth between the hole edge and the specimen side edges, and end edgemay be used to define a working space for test geometry.

Bushings 205 may be inserted in the holes 201 to carry the load moreevenly. Alternatively, the holes 201 can be machined in the polymerbefore plating to provide plating in the loading holes 201. These holes201 can incorporate fillets to prevent a buildup of plating(nodulation), or the buildup of plating that would otherwise occurshould be machined off to prevent stress concentrations. Alternativehole shapes such as square, slot, and diamond can also be incorporatedin flat specimen geometries. An alternative method is to machine thetest specimen 200 before plating and mask the edges of the gage region204 before plating, thereby providing for the exposed edges along thegage region 204 and completely encapsulating the grip regions 202. Thismethod accommodates testing the specimen 200 for some thicker platingsby gripping as the encapsulated grip regions 202, which provideincreased resistance to crushing.

A range of alternate (non-flat) geometries can be used for the gripregions 202 to obtain accurate load-displacement data for platedpolymeric structures using a flat gage region 204 with exposed edges(two-dimensional stress state). One such geometry for the grip regions202 is conical, wherein the flat grip regions 202 of the test specimen200 may be reconfigured into conically-shaped grip regions (not shown)on each end of the narrow middle gauge region of the test specimen 200,thereby accommodating loading by conical grips. In an I-beamconfiguration, a flat tensile specimen like that shown at 200 in FIG. 4is provided, but with transverse members at or near the end of specimeninstead of the conventional grip portions 202 shown in FIG. 4. Thetransverse members may be used to load the specimen using a clevis,hooks, loops, ledges, etc. This method can also accommodate flatsections or rods as the protruding components of the I-beam. In a flaredconfiguration, a flat tensile specimen with flared edges at the endsthereof may provide for gripping using platens set at angles, therebyproviding a hybrid between standard tensile grips and conical grips. Ifany sections of the test specimen geometries are prone to developporosity during a molding process (e.g., injection molding), they can behollowed out before forming. Further, reinforcing ribs can be added tohollow sections, as necessary, to prevent failure in grip areas.

Suitable test specimens may also be fabricated from composite layupstructures having a plurality of layers or plies, at least some of whichinclude reinforcing fibers. Turning to FIGS. 5-13, various layers 220,230, 240, 250, 260, 270, 280, 290, 300 of possible composite layupstructures are shown. FIG. 5 illustrates a problem created when holes201 are drilled or punched through grip regions 202 through whichreinforcing fibers 211 pass. Specifically, on the left side of FIG. 5,the creation of the hole 201 results in a number of the fibers 211 beingcut or broken, resulting in a high amount of shear transfer required totransfer the load around the hole 201. Referring to the hole 201 shownat the left in FIG. 5, it is extremely likely that a tensile specimenfabricated from the layer 220 would fail near the hole 201 shown at theleft in FIG. 5. As a solution to this problem, the fibers 211 arerearranged on the right side of the layer 220 shown in FIG. 5.Specifically, the fibers 211 are arranged so they wrap or extend aroundthe hole 201 shown at the right in FIG. 5 (see also FIGS. 6, 9-10). Thefibers 211 that extend around the hole 201 shown at the right in FIG. 5are able to take the bearing load when accommodated by symmetric fibers,as shown in FIG. 6. The layer 230 shown in FIG. 6 would complement alayer such as that shown at 220 in FIG. 5 because the fibers 211 wraparound the holes 201 in opposite directions and therefore the layers220, 230 could be used as alternating layers in a composite layupstructure.

Similarly, the layers 240, 250 of FIGS. 7-8 respectively couldcomplement each other if used as alternating plies in a composite layupstructure as the layer 240 includes fibers 211 that extendlongitudinally through the layer 240 and around the holes 201 in a Yarrangement. To complement the arrangement shown in the layer 240 ofFIG. 7, fibers 211 that extend transversely to a longitudinal axis ofthe layer 250 are shown in FIG. 8. Thus, the fibers 211 of FIG. 8 extendsubstantially transversely to the fibers 211 of FIG. 7 and therefore thelayers 240 and 250, when used as alternating layers in a composite layupstructure, are able to complement each other and provide resistance totearing at the bearing hole. Similarly, such a complementary, transverserelationship may be created by using the layers 260, 270 of FIGS. 9-10in an alternating fashion. Another example of suitable alternating pliesor layers is illustrated by the layers 280 and 290 of FIGS. 11-12 (±45°)as well as the layers 250 and 300 of FIGS. 8 and 13 (0.90°).

Thus, composite materials may be used as a substrate that is plated toform a lightweight but strong metallic part, such as a case, duct,housing, enclosure, panel, etc. Other metallic parts that can befabricated from a shaped composite article or substrate that is platedwith one or more metallic layers will be apparent to those skilled inthe art.

Brush Plating for Repair of Plated Polymer Parts

The interfacial strength between the plating and polymer materials in aplated polymeric structure is the weak point and can be structurallylimiting. When plating does not adhere to the polymeric substrate, dueto activation problems, contamination, etc., or if the plating getsnicked, dented or scratched, it can be cost effective to repair theplated polymer component rather than scrapping it. To repair a platedpolymer part or component, brush plating or brush electroplating may beemployed.

In brush plating, localized areas or entire parts may be plated using abrush saturated with plating solution. The brush is typically astainless steel or graphite body wrapped with a cloth material that bothholds the plating solution and prevents direct contact with the partbeing plated. The brush connects to the positive side of a low voltagedirect-current power source, and the item to be plated connected to thenegative side. Solution is pumped through a plating wand to maintain afresh supply of solution. The operator dips the brush in the platingsolution and then applies the brush to the part, moving the brushcontinually to get an even distribution of the plating solution over thepart. Brush electroplating has several advantages over tank plating,including portability and ability to plate parts that for some reasoncannot be tank plated, such as very large parts. Brush electroplatinginvolves little or no masking requirements and uses comparatively littleplating solution. Disadvantages compared to tank plating can includegreater operator involvement (tank plating can frequently be done withminimal attention), and the inability to achieve as great a platethickness.

The mechanics of brush plating are relatively straightforward. A110-volt AC power pack converts the voltage into DC current. A groundcable carrying a negative charge is connected to the article beingplated, which renders the article as the cathode. A second cable iscarrying a positive charge is connected to the brush or plating tool,which makes it the anode. The brush is wrapped in an absorbent material,which holds the plating solution between the anode (the brush) and thecathode (the article being plated). Electrical current travels from thebrush, through the plating solution to the work area on the articlebeing plated. Plating occurs only when and where the brush contacts thearticle. Little to no heat is generated throughout the plating process,therefore no internal stress or heat distortions are imparted to thearticle. The metallic layer is dense, hard, corrosion resistant andmetallurgically sound.

A closely related process is brush electroplating. In brushelectroplating, an article is also plated using a brush saturated with aplating solution. The brush is typically made of stainless steel andwrapped with a cloth material that holds the plating solution. The clothas prevents direct contact between the stainless steel brush and theitem being plated. The brush is connected to the positive side of a lowvoltage DC power source, and the article to be plated is connected tothe negative side of the DC power source. After the brush is dipped inthe plating solution, the brush is moved continually over the surface ofthe article to achieve an even distribution of the plating material toform a metallic layer. The brush as the anode, typically does notcontribute any plating material.

Repairing damaged areas of plated polymer components and restoring fullmembrane strength of the plating using an economical brush platingprocess can mean cost savings, extended service life and improvedphysical appearance of the part.

Use of Brush Plating in the Balancing of Polymer Components and PlatedPolymer Components

Rotating components, such as tires, spinners and fan platforms,typically must be balanced. The balancing of a rotating component isoften achieved by attaching a metal weight or bonding one or moreweights to an interior of the component. Currently, one balance methodis to use metal powder filled resins as balance “putty” and this puttymay be bonded to the component. Disclosed herein are brush plating andbrush electroplating techniques, which can be used to balance rotatingcomponents.

In brush plating, localized areas or entire parts may be plated using abrush saturated with plating solution. The brush is typically astainless steel or graphite body wrapped with a cloth material that bothholds the plating solution and prevents direct contact with the partbeing plated. The brush connects to the positive side of a low voltagedirect-current power source, and the item to be plated connected to thenegative side. Solution is pumped through a plating wand to maintain afresh supply of solution. The operator dips the brush in the platingsolution and then applies the brush to the part, moving the brushcontinually to get an even distribution of the plating solution over thepart. Brush electroplating has several advantages over tank plating,including portability and ability to plate parts that for some reasoncannot be tank plated, such as very large parts. Brush electroplatinginvolves little or no masking requirements and uses comparatively littleplating solution. Disadvantages compared to tank plating can includegreater operator involvement (tank plating can frequently be done withminimal attention), and the inability to achieve as great a platethickness.

The mechanics of brush plating are relatively straightforward. A110-volt AC power pack converts the voltage into DC current. A groundcable carrying a negative charge is connected to the article beingplated, which renders the article as the cathode. A second cable iscarrying a positive charge is connected to the brush or plating tool,which makes it the anode. The brush is wrapped in an absorbent material,which holds the plating solution between the anode (the brush) and thecathode (the article being plated). Electrical current travels from thebrush, through the plating solution to the work area on the articlebeing plated. Plating occurs only when and where the brush contacts thearticle. Little to no heat is generated throughout the plating process,therefore no internal stress or heat distortions are imparted to thearticle. The metallic layer is dense, hard, corrosion resistant andmetallurgically sound.

A closely related process is brush electroplating. In brushelectroplating, an article is also plated using a brush saturated with aplating solution. The brush is typically made of stainless steel andwrapped with a cloth material that holds the plating solution. The clothas prevents direct contact between the stainless steel brush and theitem being plated. The brush is connected to the positive side of a lowvoltage DC power source, and the article to be plated is connected tothe negative side of the DC power source. After the brush is dipped inthe plating solution, the brush is moved continually over the surface ofthe article to achieve an even distribution of the plating material toform a metallic layer. The brush as the anode, typically does notcontribute any plating material.

Thus, brush plating and/or brush electroplating may be used toselectively plate a component, while it is rotating, or in-situ. Brushplating and brush electroplating are performed much faster thanconventional plating (about 10 mils per hour) and provides ahigher-strength bond than an adhesive. The exact thickness of theplating required may depend on the density of the weight, and the properdensity the weight and the mass of the weight required to balance thecomponent can be determined prior to the brush plating.

An alternate method may be to fix a balance weight (metal, polymer, orany other material) in place on the rotatable component, and use in-situbrushed plating to permanently entrap the weight onto the component. Theplating layer(s) may extend beyond the weight, entrapping the weightagainst the rotating component, while providing superior bonding of theweight to the component as the plating layer is bonded to both theweight and the substrate.

INDUSTRIAL APPLICABILITY

Various means for forming lightweight metal parts or hollow metal partsare disclosed. A polymer suitable for being plated is selected andformed into an article of a desired shape by injection-molding,blow-molding, compression-molding or additive manufacturing. The outersurface of the formed article may be prepared for receiving a catalystvia etching, abrading, reactive ion etching, deposition of a conductivematerial, etc. Depending upon the process utilized to prepare thepolymeric substrate, the outer surface may need to be rinsed orsubjected to a neutralizing solution. Then, the outer surface may beactivated with a catalyst such as palladium. Optionally, an acceleratormay be applied before an electroless plating of a first layer of metalonto the outer surface of the formed polymers is carried out to form ametallic structure. The first layer of metal is typically electrolessnickel. Then, if electroless nickel is not the desired material for thefinished product or if the desired thickness has not been reached, anoptional second layer of metal may be electrolytically plated onto thestructure wherein the second layer of metal may typically be copper. Ifthe desired thickness has not been reached or a different metal isdesired for the final structure, one or more optional metallic layersmay be applied to the structure. The additional metallic layer(s) may beapplied via electroplating, electroless plating, electroforming, thermalspray coating, plasma vapor deposition, chemical vapor deposition, coldspraying, or, to the extent applicable, combinations thereof.

The polymer may be evacuated from the formed structure using an openingintegral to the structure or through a hole formed in the structure. Thepolymer may be evacuated by etching, melting, applications of strongbase and/or stripping agents or another suitable process as will beapparent to those skilled in the art. The hole(s) may then be pluggedand additional metallic layers may be deposited onto the structure. Aheat treatment may be carried out which may alloy or produce certaindesired metallurgical reactions (these reactions include, but are notlimited to the formation of inter-metal phases, solution treating, andprecipitation hardening) in the layer(s). This heat treatment may becarried out in the form of transient liquid phase bonding, brazing,diffusion bonding, or other processes that will be apparent to thoseskilled in the art.

What is claimed is:
 1. A method for balancing a rotatable component, themethod comprising: rotating the component; and selectively plating therotating component to deposit a metal layer onto the component until thecomponent is balanced, wherein the plating is selected from the groupconsisting of brush plating and brush electroplating.
 2. The method ofclaim 1 wherein the brush plating comprises a brush saturated withplating solution.
 3. The method of claim 2 wherein the brush is selectedfrom the group consisting of stainless steel or graphite.
 4. The methodof claim 3 wherein the brush is further wrapped with a cloth materialthat holds the plating solution and prevents direct contact with thecomponent being plated.
 5. The method of claim 1 wherein the brushelectroplating comprises a brush saturated with plating solution.
 6. Themethod of claim 5 wherein the brush is selected from the groupconsisting of stainless steel or graphite.
 7. The method of claim 6wherein the brush is further wrapped with a cloth material that holdsthe plating solution and prevents direct contact with the componentbeing plated.
 8. A method for balancing a rotatable component, themethod comprising: attaching a balancing weight to the rotatablecomponent; rotating the component; and selectively plating the rotatingcomponent and the balancing weight to deposit a metal layer onto thebalancing weight and the component until the component is balanced,wherein the plating is selected from the group consisting of brushplating and brush electroplating.
 9. The method of claim 8 wherein thebrush plating comprises a brush saturated with plating solution.
 10. Themethod of claim 9 wherein the brush is selected from the groupconsisting of stainless steel or graphite.
 11. The method of claim 10wherein the brush is further wrapped with a cloth material that holdsthe plating solution and prevents direct contact with the componentbeing plated.
 12. The method of claim 8 wherein the brush electroplatingcomprises a brush saturated with plating solution.
 13. The method ofclaim 9 wherein the brush is selected from the group consisting ofstainless steel or graphite.
 14. The method of claim 10 wherein thebrush is further wrapped with a cloth material that holds the platingsolution and prevents direct contact with the part being plated.
 15. Themethod of claim 8 wherein the balancing weight is selected from thegroup consisting of metals, metal powder filled resins and polymers. 16.A method for balancing a rotatable fan assembly, the method comprising:attaching a balancing weight to the fan assembly; rotating the fanassembly; and plating the fan assembly and the balancing weight todeposit a metal layer onto the balancing weight and fan assembly untilthe fan assembly is balanced, wherein the plating is selected from thegroup consisting of brush plating and brush electroplating.
 17. Themethod of claim 16 wherein the balancing weight is selected from thegroup consisting of metals, metal powder filled resins and polymers.